Rename plane to basis

[axelpale]

The purpose for plane2 and especially for plane3 is somewhat mixed. While being 2D plane in 3D space, plane3 also provides a reference frame for 3D objects which are not necessarily on the plane. This causes confusion in terminology: the phrase "on the plane" can mean that either the object is on the reference frame spanned by the plane basis OR the object is actually located on the plane.

Furthermore, in various places, for example in projectTo and projectFrom functions, the plane parameter is named as "basis" already.

Therefore it would make sense to either rename "plane" geometries as "basis" or fork "basis" from current plane geometries and drop any notions of basis being a flat surface. This would make the terminology more solid and avoid confusion down the line.